Method for setting starting position of data channel in wireless communication system and device using method

ABSTRACT

Provided are a method for setting a starting position in a time domain of a data channel in a wireless communication system and a device using the method thereof. The method comprises the steps of: receiving position information notifying the position at which data channels start in a plurality of subframes; receiving a control channel in a first downlink subframe; and receiving at least one data channel scheduled by the control channel in the plurality of the downlink subframes, wherein the position at which the data channel starts in the plurality of the downlink subframes is determined on the basis of the position information.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation application of U.S. patentapplication Ser. No. 14/350,530 filed Apr. 8, 2014, which is a NationalStage Application of International Application No. PCT/KR2012/008172filed Oct. 9, 2012, which claims priority to U.S. ProvisionalApplication No. 61/545,194 filed Oct. 9, 2011, all of which areincorporated by reference for all purposes as if fully set forth herein.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to wireless communication and moreparticularly, a method for setting a starting position of a data channelin a wireless communication system and apparatus using the method.

Related Art

A wireless communication system is capable of transmitting a control anda data channel simultaneously within one time interval, for example, onesubframe, which is a scheduling unit. The control channel transmitscontrol information, which includes a physical downlink control channel(PDCCH) transmitting downlink scheduling information and uplinkscheduling information. The data channel transmits control informationand/or data, which includes a Physical Downlink Shared Channel (PDSCH)and a Physical Uplink Shared Channel (PUSCH).

The amount of radio resources occupied by the control channel and thatoccupied by the data channel can be varied for each subframe. It iscommon in the Long Term Evolution (LTE) system that the area in the timedomain occupied by the control channel is figured out through a PhysicalControl Format Indication Channel (PCFICH), and a terminal considers anarea within a subframe excluding the area occupied by the controlchannel as the area occupied by the data channel.

Meanwhile, in a wireless communication system, a data channel located inone time interval (for example, a subframe) can be scheduled through onecontrol channel, or a data channel spanning a plurality of timeintervals can be scheduled through one control channel. In the lattercase, for example, a control channel transmitted at a subframe n caninclude scheduling information for scheduling data channels spanningsubframes n to n+m (where m is a natural number larger than 1).

In this case, a terminal attempts to figure out a starting position of adata channel of each subframe by decoding a total of m+1 PCFICHs fromsubframes n to n+m. If a decoding error occurs in any one of the m+1PCFICHs, however, the starting position of the data channel in thecorresponding subframe will be incorrectly identified, and as a result,all of the data from the subframes n to n+m may not be decoded properly.

SUMMARY OF THE INVENTION

The present invention has been made in an effort to provide a method forsetting a starting position of a data channel in a wirelesscommunication system and an apparatus using the method.

According to one aspect of the present invention, a method for setting astarting position of a data channel in the time domain is provided in awireless communication system. The method comprises receiving positioninformation informing of starting positions of data channels in aplurality of subframes; receiving a control channel from a firstdownlink subframe; and receiving at least one data channel scheduled bythe control channel from the plurality of downlink subframes, wherestarting positions of data channels in the plurality of downlinksubframes are determined on the basis of the position information.

A User Equipment (UE) according to another aspect of the presentinvention comprises a Radio Frequency (RF) unit transmitting andreceiving radio signals; and a processor connected to the RF unit, wherethe processor receives position information informing of startingpositions of data channels in a plurality of subframes, receives acontrol channel from a first downlink subframe, and receives at leastone data channel scheduled by the control channel from the plurality ofdownlink subframes; and starting positions of data channels in theplurality of downlink subframes are determined on the basis of theposition information.

According to the present invention, starting positions of data channelscan be set correctly even when data channels located in a plurality oftime intervals are scheduled through one control channel. Therefore, awireless communication system can select a scheduling method appropriatefor an immediate situation and reduce the possibility of occurrence oferror, thereby improving system efficiency.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a structure of a radio frame;

FIG. 2 illustrates one example of a resource grid about one downlinkslot;

FIG. 3 illustrates an example of the existing downlink subframestructure;

FIG. 4 is one example of a subframe having an ePDCCH;

FIG. 5 illustrates a structure of a uplink subframe;

FIG. 6 is a comparison example between the existing single carrier wavesystem and a carrier aggregation system;

FIG. 7 illustrates a scheduling example when cross carrier scheduling isconfigured for a carrier aggregation system;

FIG. 8 illustrates a case where data channels located in a plurality ofsubframes are scheduled by one control channel;

FIG. 9 illustrates one example of applying the method 1; and

FIG. 10 illustrates a structure of a base station and a UE according toan embodiment of the present invention.

FIG. 11 is a diagram illustrating an example of a method of determining,by a user equipment, a starting position of a data channel in accordancewith one embodiment of the present invention.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

The 3GPP (3rd Generation Partnership Project) LTE (Long Term Evolution)specifications form part of the E-UMTS (Evolved UMTS) employing theEvolved-UMTS Terrestrial Radio Access (E-UTRA), employing OrthogonalFrequency Division Multiple Access (OFDMA) for downlink transmissionwhile Single Carrier-Frequency Division Multiple Access (SC-FDMA) foruplink transmission. The LTE-Advanced (LTE-A) is the advanced form ofthe 3GPP LTE. To clarify descriptions below, this document concentrateson the 3GPP LTE/LTE-A technology; however, the technical principles ofthe present invention are not limited to the technology above.

A wireless communication system includes at least one Base Station (BS).Each base station provides a communication service covering a particulargeographic region. A geographic region can be again divided into aplurality of sub-regions. A base station usually denotes a fixed stationcommunicating with terminals and can be called in various ways such asan evolved NodeB (eNB), Base Transceiver System (BTS), access point, andAccess Network (AN).

A UE may be fixed or mobile and can be called in various ways such as aMobile Station (MS), User Terminal (UT), Subscriber Station (SS),wireless device, Personal Digital Assistance (PDA), wireless modem,handheld device, and Access Terminal (AT).

Hereinafter, the downlink implies communication from the BS to the UE,and the uplink implies communication from the UE to the BS.

A wireless communication system can correspond to a system supportingtwo-way communication. Two-way communication can be carried out byemploying a Time Division Duplex (TDD) mode, Frequency Division Duplex(FDD) mode, and so on. TDD mode uses different time resources for uplinkand downlink transmission respectively. FDD mode uses differentfrequency resources for uplink and downlink transmission respectively. Abase station and UEs can communicate with each other by using radioresources called radio frames.

FIG. 1 illustrates a structure of a radio frame.

With reference to FIG. 1, a radio frame (it can be called a frame forshort) comprises 10 subframes in the time domain, and one subframeconsists of two slots in the time domain. Length of one subframe canamount to 1 ms, and length of one slot can be 0.5 ms. Time required totransmit one subframe is called a Transmission Time Interval (TTI). ATTI can be the minimum unit for scheduling.

A single slot can include a plurality of Orthogonal Frequency DivisionMultiplexing (OFDM) symbols in the time domain. Since the 3GPP LTE usesOFDMA for downlink transmission, one symbol period is represented by anOFDM symbol. The OFDM symbol can be called in other ways according to amultiple access method. For example, if SC-FDMA is employed for a uplinkmultiple-access method, the OFDM symbol can be called an SC-FDMA symbol.Although this document assumes that a single slot contains 7 OFDMsymbols, the number of OFDM symbols included in one slot can be variedaccording to the length of a Cyclic Prefix (CP). According to the 3GPPTS 36.211 V8.5.0 (2008-12), one subframe comprises 7 OFDM symbols in thecase of normal CP while one subframe comprises 6 OFDM symbols in thecase of extended CP. The structure of a radio frame above is only anexample, and the number of subframes included in a radio frame and thenumber of slots included in a subframe can be changed in various ways.

FIG. 2 illustrates one example of a resource grid about one downlinkslot.

With reference to FIG. 2, a downlink slot includes a plurality of OFDMsymbols in the time domain and includes N_(RB) Resource Blocks (RBs) inthe frequency domain. A resource block, which is a unit of resourceallocation, includes one slot in the time domain and a plurality ofconsecutive subcarriers in the frequency domain. The number of resourceblocks N_(RB) included in a downlink slot belongs to the downlinktransmission bandwidth defined in a cell. For example, in the LTEsystem, N_(RB) may correspond to one of numbers ranging from 6 to 110.The structure of a uplink slot can be the same as that of the downlinkslot.

Each element of a resource grid is called a resource element. A resourceelement in a resource grid can be identified by an index pair (k, l)within a slot. Here, k (k=0, . . . , N_(RB)×12-1) stands for asubcarrier index of the frequency domain while l (l=0, . . . , 6) anOFDM symbol index of the time domain.

Although it was assumed in FIG. 2 that a resource block includes 7 OFDMsymbols in the time domain and 7×12 resource elements consisting of 12subcarriers in the frequency domain, the number of OFDM symbols within aresource block and the number of subcarriers are not limited to theabove example. The number of OFDM symbols and the number of subcarriersmay be changed in various ways depending on the length of CP, frequencyspacing, and the like. The number of subcarriers for a single OFDMsymbol may assume one of 128, 256, 512, 1024, 1536, and 2048.

FIG. 3 illustrates an example of the existing downlink subframestructure.

A subframe includes two consecutive slots. A maximum of three precedingOFDM symbols (a maximum of four OFDM symbols depending on a frequencyband) of a first slot within a downlink subframe corresponds to acontrol region to which a control channel is allocated while theremaining OFDM symbols correspond to a data region to which a datachannel is allocated. At this time, that a control region includes threeOFDM symbols is just an example.

Control channels such as a Physical Downlink Control Channel (PDCCH),Physical Control Format Indicator Channel (PCFICH), and Physical HybridARQ Indicator Channel (PHICH) can be allocated to the control region. AUE can read data transmitted through a data channel by decoding controlinformation transmitted through the PDCCH. The number of OFDM symbolsincluded in the control region within a subframe can be known throughthe PCFICH. The PHICH carries a Hybrid Automatic Repeat reQuest (HARQ)Acknowledgement (ACK)/Non-acknowledgement (NACK) signal in response touplink transmission.

A Physical Downlink Shared Channel (PDSCH) can be allocated to the dataregion. In what follows, a radio resource region to which a particularchannel is transmitted can be called a particular channel region. Forexample, the region to which the PDCCH is transmitted can be called aPDCCH region, and the region to which the PDSCH is transmitted can becalled a PDSCH region.

[Structure of PDCCH]

The control region comprises a plurality of Control Channel Elements(CCEs), which form a series of logical CCEs. A CCE corresponds to aplurality of Resource Element Group (REG). For example, a CCE cancorrespond to 9 REGs. An REG is used to define mapping of a controlchannel into resource elements. For example, one REG can comprise fourresource elements. A series of CCEs is a set of the whole CCEs forming acontrol region within a single subframe.

Within a control region, a plurality of PDCCHs can be transmitted. APDCCH is transmitted on an aggregation of one or a few consecutive CCEs.According to the number of CCEs which form a CCE aggregation, a formatof the PDCCH and the number of available bits for the PDCCH aredetermined. In what follows, the number of CCEs used for PDCCHtransmission is called a CCE aggregation level L. Also, a CCEaggregation level is a CCE unit meant for searching for a PDCCH. Thesize of a CCE aggregation level is defined by the number neighboringCCEs. For example, a CCE aggregation level can be defined to have 1, 2,4, or 8 CCEs.

The following table shows examples of a format of the PDCCH and thenumber of available bits for the PDCCH according to a CCE aggregationlevel.

TABLE 1 PDCCH CCE aggregation Number of Number of format level REGsPDCCH bits 0 1 9 72 1 2 18 144 2 4 36 288 3 8 72 576

The control information transmitted through the PDCCH is called DownlinkControl Information (DCI). DCI transmits uplink scheduling information(which is called a UpLink (UL) grant); downlink scheduling information(which is called a DownLink (DL) grant); or uplink power controlcommand, control information for paging, and control information forspecifying a random access (RACH) response.

DCI can be transmitted according to a predetermined format, and anintended use of the DCI can be defined by the corresponding DCI format.For example, uses of the respective DCI formats can be listed up asshown in the table below.

TABLE 2 DCI format Use DCI format 0 PUSCH scheduling DCI format 1Scheduling of one PDSCH codeword DCI format 1A Compact scheduling and arandom access process of one PDSCH codeword DCI format 1B Compactscheduling of one PDSCH codeword having precoding information DCI format1C Very compact scheduling of one PDSCH codeword DCI format 1D Compactscheduling of one PDSCH codeword having precoding and power offsetinformation DCI format 2 PDSCH scheduling of UEs configured for closedloop spatial multiplexing mode DCI format 2A PDSCH scheduling of UEsconfigured for open loop spatial multiplexing mode DCI format 3Transmission of a TPC command of a PUCCH and PUSCH having two bit poweradjustment DCI format 3A Transmission of a TPC command of a PUCCH andPUSCH having one bit power adjustment DCI format 4 PUSCH scheduling inone UL cell under multiple antenna transmission mode

The PDCCH can be generated through the following procedure. A basestation adds a Cyclic Redundancy Check (CRC) for error detection to theDCI to be sent to a UE. The CRC is masked with an identifier dependingon an owner of the PDCCH or intended use of the PDCCH, which is called aRadio Network Temporary Identifier (RNTI). As for the PDCCH meant for aparticular UE, a unique identifier for the UE assigned from the basestation, the CRC can be masked with Cell-RNTI (C-RNTI), for example.Similarly, the CRC can be masked with a paging identifier, for example,Paging-RNTI (P-RNTI) in the case of a PDCCH meant for a paging messagetransmitted through a Paging Channel (PCH). The CRC can be masked with asystem information identifier, for example, System Information-RNTI(SI-RNTI) in the case of a PDCCH meant for system informationtransmitted through a Downlink Shared Channel (DL-SCH). The CRC can bemasked with a Random Access-RNTI (RA-RNTI) in the case of a PDCCH meantfor designating a random access response in response to transmission ofa random access preamble of the UE. If a C-RNTI is used, the PDCCHcarries control information for the corresponding particular UE while,if a different RNTI is used, the PDCCH carries common controlinformation received by all of the UEs within a cell.

Next, the base station generates coded data by carrying out channelcoding on the control information to which the CRC pattern has beenadded. And the base station carries out rate matching according to a CCEaggregation level assigned to the PDCCH format. Next, the base stationmodulates coded data to generate modulation symbols. At this time, thenumber of modulation symbols constituting one CCE can be variedaccording to the CCE aggregation level (one from among 1, 2, 4, 8). Themodulation symbols are mapped to physical resource elements (namely, CCEto RE mapping is carried out).

In the 3GPP LTE system, the UE uses blind decoding for detection of aPDCCH. Blind decoding carries out demasking of a CRC of a received PDCCH(which is called a candidate PDCCH) with a desired identifier and checksa CRC error to see whether the corresponding PDCCH is a control channelfor the UE. The rationale for the UE to carry out blind decoding is thatit does not know beforehand at which position within a control regionits PDCCH is transmitted based on which CCE aggregation level or whichDCI format.

As described in detail above, a plurality of PDCCHs can be transmittedwithin one subframe, and the UE monitors the plurality of PDCCHs foreach subframe. At this time, monitoring refers to the UE's attempt todecode the PDCCH according to the PDCCH format.

The 3GPP LTE system uses a Search Space (SS) to reduce the burden fromblind decoding. A search space can be regarded as a monitoring set of aCCE for PDCCH. The UE monitors a PDCCH within the corresponding searchspace.

A search space is divided into a Common Search Space (CSS) and aUE-specific Search Space (USS or SS in a simplified notation). A CSS isa space in which a search for PDCCH having common control information iscarried out, which can comprise 16 CCEs with CCE indices ranging from 0to 15 and support a PDCCH with a CCE aggregation level of 4 or 8. TheCSS is made to be known to all of the UEs inside a cell, and each UEsearches the CSS for the DCI format 1A, 1C, 3, and 3A. A PDCCH whichcarries UE-specific information can also be transmitted to the CSS.

A USS is defined for each UE and supports a PDCCH having a CCEaggregation level of {1, 2, 4, 8}. The UE is not required to search forall of the defined DCI formats simultaneously. This is intended toreduce the number of attempts for blind decoding. The UE always searchesfor the DCI format 0 and 1A which have the same length with each otherin the USS and are distinguished by a 1-bit flag. The UE additionallysearches for the DCI format 1, 1B, and 2 according to a currenttransmission mode. The transmission mode will be described later.

The starting position of a search space is defined differently for theCSS and USS. The starting position of the CSS is fixed regardless of asubframe, but the starting position of the USS can be varied for eachsubframe, depending on a UE identifier (for example, C-RNTI), CCEaggregation level and/or slot number within a radio frame. In case thestarting position of the USS is located in the CSS, the USS and the CSScan overlap with each other.

In a CCE aggregation level Lε{1, 2, 3, 4}, a search space S^((L)) _(k)can be defined as a set of candidate PDCCHs. The CCE corresponding to acandidate PDCCH m of the search space S^((L)) _(k) is given as follows.

L·{(Y _(k) +m)mod └N _(CCE,k) /L┘}+i  [Equation. 1]

where i=0, 1, . . . , L−1; m=0, . . . , M^((L))−1, N_(CCE,K) representsthe total number of CCEs that can be used for transmission of a PDCCHwithin a control region of a subframe k. The control region includes aset of CCEs indexed from 0 to N_(CCE,K). M^((L)) represents the numberof candidate PDCCHs at the CCE aggregation level L in a given searchspace. In the CSS, Y_(k) is set to 0 for two aggregation levels, namelyL=4 and L=8. In the USS at a CCE aggregation level L, the variable Y_(k)is defined as follows.

Y _(k)=(A·Y _(k-1))mod D  [Equation. 2]

where Y_(—1)=nRNTI≠0, A=39827, D=65537, k=floor(n_(s)/2), n_(s)represents a slot number within a radio frame. The floor functionfloor(x) gives the largest integer less than or equal to x.

The following table represents the number of candidate PDCCHs in asearch space.

TABLE 3 Number of Number of PDCCH Number of candidate PDCCHs candidatePDCCHs format CCEs in the CSS in the USS 0 1 — 6 1 2 — 6 2 4 4 2 3 8 2 2

Meanwhile, nine downlink transmission modes can be defined between thebase station and the UE. Depending on the downlink transmission mode,the number of codewords or transport blocks (TBs) included in a PDSCHwithin each subframe can be varied.

Transmission mode 1: mode where no precoding is employed (single antennaport transmission mode)

Transmission mode 2: transmission mode that can be used for two or fourantenna ports using Space-Frequency Block Coding (SFBC) (transmissiondiversity)

Transmission mode 3: open-loop mode capable of rank adaptation based onRank Indication (RI) feedback (open loop spatial multiplexing). In casethe rank is 1, transmission diversity can be applied, and in case therank is larger than 1, large delay Cyclic Delay Diversity (CDD) can beused.

Transmission mode 4: mode to which precoding feedback supporting dynamicrank adaptation is applied (closed-loop spatial multiplexing).

Transmission mode 5: multi-user MIMO

Transmission mode 6: closed-loop rank 1 precoding

Transmission mode 7: mode in which a UE-specific reference signal isused

Transmission mode 8: dual layer transmission using antenna ports 7 and8; or signal antenna port transmission using an antenna port 7 or 8.

Transmission mode 9: transmission of a maximum of 8 layers by usingantenna ports 7 to 14.

Meanwhile, a wireless communication system can define and use a newcontrol channel within a PDSCH region. The new control channel is calledan extended PDCCH or enhanced PDCCH (ePDCCH) for the purposed ofconvenience.

FIG. 4 is one example of a subframe having an ePDCCH.

The PDCCH carrying various kinds of control information such as DL/ULscheduling in the existing 3GPP LTE/LTE-A system is transmitted only tothe control region of a subframe. In this regard, introduction of anePDCCH which can be scheduled more flexibly is under consideration. TheePDCCH is also called the enhanced PDCCH.

A subframe comprises a PDCCH region 410 for monitoring a PDCCH and oneor more ePDCCH regions 420, 430 for monitoring ePDCCHs.

The PDCCH region 410 is located only within a maximum of four precedingOFDM symbols of a subframe whereas the ePDCCH region 420, 430 can bescheduled flexibly within a data region.

In the PDCCH region 410, the PDCCH can be demodulated on the basis of aCell-specific Reference Signal (CRS). In the ePDCCH region 420, 430, theePDCCH can be demodulated on the basis of a User equipment-specificReference Signal (URS). A URS can be transmitted from the correspondingePDCCH region 420, 430.

A CRS can be received by all of the UEs within a cell, which is areference signal transmitted throughout the whole downlink bandwidth. AnRS sequence r_(1, ns)(m) for the CRS can be defined as follows.

$\begin{matrix}{{r_{l,n_{s}}(m)} = {{\frac{1}{\sqrt{2}}\left( {1 - {2 \cdot {c\left( {2\; m} \right)}}} \right)} + {j\frac{1}{\sqrt{2}}\left( {1 - {2 \cdot {c\left( {{2\; m} + 1} \right)}}} \right)}}} & \left\lbrack {{Equation}.\mspace{14mu} 3} \right\rbrack\end{matrix}$

where m=0, 1, . . . , 2N_(maxRB)−1, N_(maxRB) is the maximum number ofRBs; ns is the slot number within a radio frame; and 1 is the OFDMsymbol number within the slot.

A pseudo-random sequence c(i) is defined by a Gold sequence of length 31as shown below.

c(n)=(x ₁(n+N _(C))+x ₂(n+N _(C)))mod 2

x ₁(n+31)=(x ₁(n+3)+x ₁(n))mod 2

x ₂(n+31)=(x ₂(n+3)+x ₂(n+2)+x ₂(n+1)+(n))mod 2  [Equation. 4]

where Nc=1600 and a first m-sequence is initialized as follows: x1(0)=1,x1(n)=0, m=1, 2, . . . , 30.

A second m-sequence is initialized at the start position of each OFDMsymbol so that c_(init)=2¹⁰(7(ns+1)+1+1)(2N^(cell) _(ID)+1)±2N^(cell)_(ID)+N_(CP). N^(cell) ID is a Physical Cell Identity (PCI), and in anormal CP, N_(CP)=1 while N_(CP)=0 in the case of an extended CP.

Although a CRS is transmitted throughout the whole region of a subframe,a URS is transmitted within a data region of the subframe and used fordemodulation of the corresponding PDSCH. The URS is also called aDedicated Reference Signal (DRS).

A URS is transmitted only in an RB to which the corresponding PDSCH ismapped.

The URS is used only by the UE which receives the corresponding PDSCH.An RS sequence r_(ns)(m) for a US is the same as Eq. 3. At this time,m=0, 1, . . . , 12 N_(PDSCH, RB)−1 and N_(PDSCH, RB) represents thenumber of RBs of the corresponding PDSCH transmission. A pseudo randomsequence generator is initialized at the starting position of eachsubframe so that c_(init)=(floor(ns/2)+1)(2N^(cell)_(ID)+1)2¹⁶+n_(RNTI). n_(RNTI) is a UE identifier.

The above description is related to the case where a URS is transmittedthrough a single antenna. When the URS is transmitted through multipleantennas, the pseudo random sequence generator is initialized at thestarting position of each subframe so thatc_(init)=(floor(ns/2)+1)(2N^(cell) _(ID)+1)2¹⁶+n_(SCID). n_(SCID) is aparameter obtained from a DL grant (for example, DCI format 2B or 2C)related to PDSCH transmission.

An ePDCCH can be monitored in the ePDCCH region 420, 430 through blinddecoding. Likewise, the ePDCCH may not use blind decoding. The UE, beaware of positions or the number of ePDCCHs within the ePDCCH region420, 430, can detect the ePDCCH at a predefined position.

One UE, a group of UEs, or UEs within a cell can monitor the ePDCCHregion 420, 430. If a particular UE monitors the ePDCCH region 420, 430,n_(RNTI) or n_(SCID), which is used for initialization of the pseudorandom sequence generator of the URS, can be obtained on the basis ofthe identifier of the particular UE. If a group of UEs monitor theePDCCH region 420, 430, n_(RNTI) or n_(SCID), which is used forinitialization of the pseudo random sequence generator of the URS, canbe obtained on the basis of the identifier of the corresponding UEgroup.

When the ePDCCH region 420, 430 is transmitted through multipleantennas, precoding which is the same as the URS can be applied to theePDCCH region 420, 430.

Since ePDCCH is more flexible than the PDCCH in terms of scheduling,transmission of the ePDCCH region can be considered in the whole of aparticular subframe. In a subframe, the PDCCH and the ePDCCH region canbe defined at the same time or either of the two regions. The ePDCCHregion can be set to a plurality of consecutive subframes ordiscontinuous subframes. Whether an ePDCCH region is set within asubframe can be indicated through a upper layer signal such as an RRCmessage or through a DCI within the existing PDCCH region.

FIG. 5 illustrates a structure of a uplink subframe.

With reference to FIG. 5, a uplink subframe can be divided into acontrol region and a data region in the frequency domain. In the controlregion, a Physical Uplink Control Channel (PUCCH) for transmittinguplink control information is allocated. A Physical Uplink SharedChannel (PUSCH) for transmitting data (depending on the needs, controlinformation can also be transmitted) is allocated in the data region.According to a particular configuration, the UE is enabled to transmitthe PUCCH and the PUSCH simultaneously or either of the two channels.

A PUCCH is allocated in the form of an RB pair in a subframe of one UE.Resource blocks belonging to an RB pair occupy subcarriers differentfrom each other respectively in a first and a second slot. The frequencyband occupied by a resource block belonging to the RB pair allocated tothe PUCCH is changed on the basis of a slot boundary. The RB pairallocated to the PUCCH as described above is then said to havefrequency-hopped at the slot boundary. Frequency diversity gain can beobtained by transmitting uplink control information through differentsubcarriers according as time passes.

The PUCCH can transmit a Hybrid Automatic Repeat reQuest (HARM)Acknowledgement (ACK)/Non-acknowledgement (NACK) and Channel StatusInformation (CSI) indicating downlink channel status such as ChannelQuality Indicator (CQI), Precoding Matrix Index (PMI), Precoding TypeIndicator (PTI), and Rank Indication (RI). Periodic channel statusinformation can be transmitted through the PUCCH.

The PUSCH is mapped to a Uplink Shared Channel (UL-SCH), which is atransport channel. Uplink data transmitted on the PUSCH may correspondto a transport block, which is a data block meant for a UL-SCHtransmitted during a TTI. The transport block can include user data. Theuplink data can correspond to multiplexed data. The multiplexed data canbe obtained from multiplexing of a transport block for the UL-SCH andchannel status information. For example, channel status informationmultiplexed into data can include CQI, PMI, RI, and so on. Also, theuplink data can comprise only channel status information. Periodic ornon-periodic channel status information can be transmitted through thePUSCH.

In a wireless communication system, a UE receives scheduling informationsuch as a DL grant and UL grant through the PDCCH and based on thescheduling information, performs an operation of receiving the PDSCH andtransmitting the PUSCH.

In general, the DL grant and PDSCH are received within the samesubframe. In the case of FDD, the PUSCH is transmitted after foursubframes from the subframe which receives the UL grant. Besides suchdynamic scheduling, the LTE system provides Semi-Persistent Scheduling(SPS), too.

Downlink or uplink SPS can inform the UE through a upper layer signalsuch as a Radio Resource Control (RRC) about which subframes performsemi-persistent transmission of PUSCH and reception of PDSCH. Aparameter given to the upper layer signal can be the period and offsetof a subframe, for example.

After recognizing semi-persistent transmission/reception through the RRCsignaling, the UE performs or releases SPS transmission/reception if theUE receives an activation signal or a release signal of SPS transmissionthrough the PDCCH. In other words, if the UE receives an activationsignal or release signal through the PDCCH, instead of immediatelyperforming SPS transmission/reception upon receiving SPS through the RRCsignaling, the UE performs SPS transmission/reception on a subframecorresponding to the subframe period and offset received through the RRCsignaling by applying frequency resources (resource blocks) according toallocation of resource blocks specified by the PDCCH, modulationaccording to MCS information, and coding rate. If a release signal isreceived through the PDCCH, the UE stops SPS transmission/reception. Ifthe PDCCH including an activation signal is received again, the stoppedSPS transmission/reception is resumed by using frequency resourcesspecified by the corresponding PDCCH, MCS, and so on.

The PDCCH for SPS setting/release can be called an SPS allocation PDCCHwhile the PDCCH for a conventional PUSCH/PDSCH can be called a dynamicPDCCH. Then the UE can perform validation of whether a PDCCH correspondsto the SPS allocation PDCCH in case the following conditions are allmet: 1) CRC parity bits obtained from a PDCCH payload are scrambled intoan SPS C-RNTI. 2) And the value of a new data indicator field should be0. Also, if each field of the PDCCH is set according to a field value inthe following table with respect to each DCI format, the UE considersthe DCI information of the corresponding PDCCH as SPS activation orrelease.

TABLE 4 DCI format DCI format DCI format 0 1/1A 2/2A/2B/2C TPC commandfor set to ‘00’ N/A N/A scheduled PUSCH Cyclic shift DM set to ‘000’ N/AN/A RS Modulation and MSB is set N/A N/A coding scheme to ‘0’ andredundancy version HARQ process N/A FDD: set to ‘000’ FDD: set to ‘000’number TDD: set to TDD: set to ‘0000’ ‘0000’ Modulation and N/A MSB isset to ‘0’ For the enabled coding scheme transport block: MSB is set to‘0’ Redundancy N/A set to ‘00’ For the enabled version transport block:set to ‘00’

The Table 4 shows field values of an SPS allocation PDCCH to performauthentication of SPS activation.

TABLE 5 DCI format 0 DCI format 1A TPC command for scheduled set to ‘00’N/A PUSCH Cyclic shift DM RS set to ‘000’ N/A Modulation and coding setto ‘11111’ N/A scheme and redundancy version Resource block assignmentSet to all ‘1’s N/A and hopping resource allocation HARQ process numberN/A FDD: set to ‘000’ TDD: set to ‘0000’ Modulation and coding N/A setto ‘11111’ scheme Redundancy version N/A set to ‘00’ Resource blockassignment N/A Set to all ‘1’s

The Table 5 shows field values of an SPS allocation PDCCH to performauthentication of SPS release.

Now, described will be a carrier aggregation system.

[Carrier Aggregation System]

FIG. 6 is a comparison example between the existing single carrier wavesystem and a carrier aggregation system.

With reference to FIG. 6(a), in a single carrier wave system, only asingle carrier (single component carrier (CC)) is supported for uplinkand downlink transmission of the UE. Bandwidth of a carrier wave mayvary but the number of carriers allocated to the UE is one. On the otherhand, in a carrier aggregation (CA) system as shown in FIG. 6(b), aplurality of component carriers (DL CC A to C, UL CC A to C) can beallocated to the UE. A component carrier refers to a carrier wave usedin a carrier aggregation system and can be called a carrier for short.For example, three component carriers, each of which having a bandwidthof 20 MHz, can be allocated to provide bandwidth of 60 MHz to the UE.

Carrier aggregation systems can be grouped into contiguous carrieraggregation systems where aggregated carriers are arranged continuouslyand non-contiguous carrier aggregation systems where aggregated carriersare separated from each other. In what follows, if a system is calledsimply a carrier aggregation system, it should be understood that thesystem includes both of the contiguous and non-contiguous componentcarriers.

When one or more component carriers are aggregated, target componentcarriers may use the same bandwidth used in the existing system toensure backward compatibility with the existing system. For example, the3GPP LTE system supports bandwidth of 1.4 MHz, 3 MHz, 5 MHz, 10 MHz, 15MHz, and 20 MHz while the 3GPP LTE-A system can establish a broadbandbeyond 20 MHz by using only the bandwidth used for the 3GPP LTE system.A broadband can be constructed by newly defining frequency bands insteadof employing the frequency band used for the existing system.

The system frequency band of a wireless communication system ischaracterized by a plurality of carrier frequencies. At this time,carrier frequency denotes center frequency of a cell. In what follows, acell may stand for downlink frequency resources and uplink frequencyresources. Also, a cell may denote a combination of downlink frequencyresources and optional uplink frequency resources. Also, in case carrieraggregation is not taken into account, one cell can always exist in theform of a pair of uplink and downlink frequency resources.

In order for data transmission and reception to be carried out through aparticular cell, the UE first has to complete configuration of theparticular cell. At this time, configuration refers to the state wherereception of system information required for data transmission andreception with respect to the corresponding cell has been completed. Forexample, configuration can include the overall procedure for receivingcommon physical layer parameters required for data transmission andreception, Media Access Control (MAC) layer parameters, or parametersrequired for a particular operation in the RRC layer. A completelyconfigured cell, once receiving information indicating that packet datacan be transmitted, is in a state where transmission and reception ofpackets can be carried out immediately.

A completely configured cell can be in an activation state or adeactivation state. At this time, activation indicates that transmissionor reception of data is being carried out or in a ready state. The UE,to check resources allocated to itself (which can be frequency or time),can monitor or receive the control (PDCCH) and the data channel (PDSCH)of an activated cell.

Deactivation refers to the state where transmission or reception oftraffic data is not possible but only measurement ortransmission/reception of minimal information is allowed. The UE canreceive system information required for packet reception from adeactivated cell. On the other hand, the UE, to check resourcesallocated to itself (which may be frequency or time), does not monitoror receive the control (PDCCH) and the data channel (PDSCH) of adeactivated cell.

Cells can be divided into primary cells, secondary cells, and servingcells.

A primary cell refers to a cell operating in the primary frequency band,a cell in which the UE performs an initial connection establishmentprocedure with the base station, a cell in which the UE performs aconnection re-establishment procedure, or a cell designated as theprimary cell during a handover procedure.

A secondary cell refers to a cell operating in the secondary frequencyband, which is configured when an RRC connection is established and usedfor providing additional radio resources.

A serving cell is composed of primary cells when carrier aggregation isnot configured for the UE or when the UE is unable to provide carrieraggregation. In case carrier aggregation is configured, the term of aserving cell represents a cell configured for the UE and can be composedof multiple cells. In the case of FDD, one serving cell can be composedof one downlink component carrier or a pair of downlink componentcarrier and uplink component carrier. A plurality of serving cells canbe composed of a set comprising a primary cell and one or more secondarycells.

A Primary Component Carrier (PCC) refers to a component carrier (CC)corresponding to a primary cell. A PCC is one of CCs, which enables theUE to establish a connection or an RRC connection with the base stationat the initial stage. A PCC is a special CC, which takes care of aconnection or an RRC connection for signaling a plurality of CCs andmanages UE context which is connection information related to the UE.Also, in case the PCC is in an RRC connected mode as the PCC isconnected to the UE, the PCC always remains in an activation state. Adownlink component carrier corresponding to the primary cell is called aDownlink Primary Component Carrier (DL PCC) while a uplink componentcarrier corresponding to the primary cell is called a Uplink PrimaryComponent Carrier (UL PCC).

A Secondary Component Carrier (SCC) refers to a CC corresponding to thesecondary cell. In other words, An SCC is a CC allocated to the UE inaddition to the PCC, which is an extended carrier meant for additionalresource allocation by the UE in addition to the PCC and stays in anactivation or deactivation state. A downlink component carriercorresponding to the secondary cell is called a Downlink SecondaryComponent Carrier (DL SCC) while a uplink component carriercorresponding to the secondary cell is called a Uplink SecondaryComponent (UL SCC).

The primary and secondary cell have the following characteristics.

First, the primary cell is used for transmission of a PUCCH. Second, theprimary cell is always activated whereas the secondary cell is activatedor deactivated depending on a particular condition. Third, when theprimary cell experiences Radio Link Failure (RLF), an RRC re-connectionis triggered. Fourth, the primary cell can be changed by change of asecurity key or a handover procedure accompanying a Random AccessCHannel (RACH) procedure. Fifth, Non-Access Stratum (NAS) information isreceived through the primary cell. Sixth, in the case of a FDD system,the primary cell is always made of a pair of a DL PCC and a UL PCC.Seventh, a different CC can be configured as the primary cell for eachUE. Eighth, the primary cell can be replaced only through a handover orcell selection/re-selection procedure. In adding a new secondary cell,RRC signaling can be used for transmitting system information of adedicated secondary cell.

Regarding CCs constituting a serving cell, a downlink component carriercan constitute one serving cell, or a downlink component carrier and auplink component carrier are configured to be connected to form oneserving cell. However, a single uplink component carrier alone cannotform a serving cell.

Activation/deactivation of a component carrier is the same concept ofactivation/deactivation of a serving cell. For example, suppose aserving cell 1 is composed of DL CC1. Then, activation of the servingcell 1 implies activation of DL CC1. If it is assumed that a servingcell 2 is composed of DL CC2 and UL CC2 connected to each other,activation of serving cell 2 implies activation of DL CC2 and UL CC2. Inthis regard, each component carrier can correspond to a serving cell.

The number of component carriers aggregated can be set differentlybetween downlink and uplink transmission. When the number of downlinkCCs and the number of uplink CCs are the same to each other, it iscalled symmetric aggregation. If the two numbers are different from eachother, it is called asymmetric aggregation. Also, sizes of CCs (namely,bandwidth) can differ from each other. For example, if five CCs areinvolved to form a frequency band of 70 MHz, the configuration of CCscan be done like 5 MHz CC (carrier #0)+20 MHz CC (carrier #1)+20 MHz CC(carrier #2)+20 MHz CC (carrier #3)+5 MHz CC (carrier #4).

As described above, different from a single carrier system, a carrieraggregation system can support a plurality of CCs, namely, multipleserving cells.

The carrier aggregation system can support cross-carrier scheduling.Cross-carrier scheduling is one of scheduling methods, which can performresource allocation of a PDSCH transmitted through a different CC byusing a PDCCH transmitted through a particular CC and/or resourceallocation of a PUSCH transmitted through a different CC other than a CClinked by default to the particular CC. In other words, a PDCCH and aPDSCH can be transmitted through downlink CCs different from each other,and a PUSCH can be transmitted through a different uplink CC other thana uplink CC linked to a downlink CC to which the PDCCH including a ULgrant has been transmitted. As indicated above, a system supportingcross-carrier scheduling requires a carrier indicator indicating a DLCC/UL CC through which the PDSCH/PUSCH receiving control informationfrom the PDCCH is transmitted. In what follows, a field containing sucha carrier indicator is called a Carrier Indication Field (CIF). The CIFvalue of the primary cell can be set to 0.

A carrier aggregation system supporting cross-carrier scheduling canincorporate a CIF into the existing Downlink Control Information (DCI)format. In a system supporting the cross-carrier scheduling, forexample, the LTE-A system, since the CIF is added to the existing DCIformat (namely, the DCI format used in the LTE system), the DCI formatcan be extended to include three additional bits. The PDCCH structurecan re-use the existing coding method, resource allocation method(namely, resource mapping based on CCE) and so on.

Meanwhile, the base station can specify a PDCCH monitoring DL CC set.The PDCCH monitoring DL CC set comprises part of DL CCs from the wholeof aggregated DL CCs; once cross-carrier scheduling is defined, the UEcarries out PDCCH monitoring/decoding only for the DL CC included in thePDCCH monitoring DL CC set. In other words, the base station transmits aPDCCH in association with the PDSCH/PUSCH that is scheduled only throughthe DL CC included in the PDCCH monitoring DL CC set. The PDCCHmonitoring DL CC set can be configured in a UE-specific, UEgroup-specific, or cell specific manner.

FIG. 7 illustrates a scheduling example when cross carrier scheduling isconfigured for a carrier aggregation system.

With respect to FIG. 7, DL CC 0, DL CC 2, and DL CC 4 form a PDCCHmonitoring DL CC set, by which the UE monitors the PDCCH. The UEsearches the CSS of DL CC 0 for the DL grant/UL grant of the DL CC 0 andUL CC 0 (the UL CC linked to the DL CC 0 by SIB2). And the UE searchesthe UE-specific search space 1 (SS 1) of the DL CC 0 for the DL grant/ULgrant of the DL CC 1 and UL CC 1. The SS 1 is one example of the USS. Inother words, the SS 1 of the DL CC 0 is a search space in which the UEsearches for the DL grant/UL grant carrying out cross carrierscheduling.

Now, the present invention is described.

A wireless communication system can schedule data channels of multiplesubframes through one control channel depending on a situation. In whatfollows, a PDCCH is used to represent the control channel and a PDSCHthe data channel, but the present invention is not limited to theaforementioned assumption.

FIG. 8 illustrates a case where data channels located in a plurality ofsubframes are scheduled by one control channel.

With reference to FIG. 8, PDSCHs located at subframe 0, 1, and 2 arescheduled through the PDCCH transmitted at subframe 0. As describedabove, scheduling of PDSCHs located at a plurality of subframes througha single PDCCH is called bundled scheduling. Bundled scheduling can alsobe interpreted such that a PDSCH of a subframe including the PDCCH andthat not including the PDCCH are scheduled at the same time through asingle PDCCH.

With reference to FIG. 8(b), a PDSCH located at subframe 2 is scheduledthrough the PDCCH transmitted at subframe 0. As described above,scheduling at least one PDSCH located at a plurality of subframes notincluding the PDCCH through a single PDCCH is called cross subframescheduling.

The bundled scheduling and cross subframe scheduling can be used beingcombined with each other, which is called cross-bundled scheduling.

At the time of applying the bundled scheduling, cross subframescheduling, or cross-bundled scheduling, the base station informs aboutthe start and the end subframe of such scheduling. Also, the basestation can command scheduling by forming a bitmap describing subframesto which the scheduling can be applied.

A conventional UE first detects a PCFICH from each downlink subframe andidentifies a PDCCH region. The UE then detects its PDCCH through blinddecoding in the identified PDCCH region. If a DL grant is found, the UEdecodes the PDSCH within the same subframe according to the DL grant.Similarly, if a UL grant is found, the UE transmits a PUSCH according tothe UL grant from the corresponding uplink subframe.

Considering the aforementioned operation of the conventional UE, if aPDCCH which schedules a PDSCH and the PDSCH scheduled by the PDCCH arelocated in the same subframe (for example, subframe 0 of FIG. 8(a)), aPCFICH is detected. When obtaining an error-free CFI through the PCFICH,the UE detects its PDCCH by identifying the PDCCH region and attempts toreceive its PDSCH by considering the remaining region of a subframeexcluding the PDCCH region as a PDSCH region.

By the way, there is a chance for an error in detecting the PCFICH, andthe UE has no means to recognize the occurrence of the error. This is sobecause the PCFICH only relies on repetition based on simplex codingwithout using CRC and provides no other means to detect an error. Inthis manner, if an error occurs in detecting the PCFICH, the UE becomesunable to detect the PDCCH itself as the CFI is mistaken for a differentvalue.

Meanwhile, if a scheduling PDCCH and a scheduled PDSCH are located insubframes different from each other (however, they can be the samesubframe), the PCFICH is detected normally in a subframe receiving thePDCCH and the PDCCH is detected. In a subframe receiving the PDSCH,however, there can be a chance that an error is developed for detectingthe PCFICH in a subframe receiving the PDSCH and the starting positionof the PDSCH is identified wrongly as a wrong CFI value is applied.

In this manner, if the starting position of the PDSCH is wronglyperceived, positions of coded bits mapped to the PDSCH are shifted; atthe time of HARQ combining, only the noise is enhanced. Therefore, aproblem of degraded data reception performance arises.

The aforementioned problem results from the fact that there is a chanceof developing an error for decoding the PCFICH after all. Such an errorcan occur, for example, when a method for reducing inter-cellinterference in units of subframes in a heterogeneous network is used.In other words, in the case of control channels setting hightransmission power as required SINR is high, the interference exerted onneighboring cells can be lowered by limiting transmission totransmission in units of subframes. This is so because decodingperformance of a control channel in a serving cell can be deteriorateddue to variation of transmission power of a control channel in theserving cell according to ABS (Almost Blank Subframe) configurationapplied to the serving cell, variation of interference of the servingcell according to the ABS configuration on neighboring cells, and so on.At this time, an ABS subframe denotes a subframe to which only a CommonReference Signal (SRS) is transmitted.

The problem of wrongly recognizing the starting position of the PDSCHregion due to the PCFICH decoding error can be resolved through thefollowing methods proposed by the present invention.

In what follows, CFID (CFI for PDSCH) denotes position information forinforming of the starting position of the PDSCH. The CFID can directlyspecify a starting OFDM symbol of the PDSCH. Or the starting position ofthe PDSCH region can be known indirectly as the number of OFDM symbolsin the PDCCH region is informed. Similarly, in case a temporalrelationship between the PDCCH region and the PDSCH region is definedbeforehand, the last symbol of the PDCCH region can be known.

I. Method 1.

The base station can inform about the starting position of a scheduledPDSCH by informing about the corresponding CFID through a higher layersignal such as an RRC message. In other words, the base station informsabout the starting position of the PDSCH in each subframe through an RRCmessage transmitted through a particular PDSCH rather than inform aboutthe starting position through the PCFICH of the corresponding subframe.This method provides high reliability in a sense that an RRC message canbe received again by using HARQ in such a case that the RRC message isnot received properly.

FIG. 9 illustrates one example of applying the method 1.

The base station provides a CFID for the UE through an RRC message S181.

The base station transmits a control channel applied for a plurality ofsubframe sections in the subframe n S182. The control channel can be thePDCCH, and the PDCCH can include scheduling information about one or twoor more PDSCHs with respect to the plurality of subframe sections asshown in FIG. 8.

The UE decodes a control channel S183.

The base station transmits a data channel from a subframe n+m, which isa subframe within the plurality of subframe sections S184. The datachannel can be a PDSCH.

The UE, based on the CFID previously received from the subframe n+m,identifies the starting position of the data channel and decodes thedata channel S185.

The CFID specified by an RRC message can be a value commonly applied forall of the subframes within the plurality of subframes. In this case,the CFID value included in the RRC message can assume one value. In casescheduling is performed by using an ePDCCH, the same value as the RRCvalue specified for the starting position of the ePDCCH can be appliedto the CFID value.

Similarly, the CFID value specified by the RRC message can be given asan independent value according to characteristics of a subframe withinthe plurality of subframe sections. For example, in a plurality ofsubframe sections, a Multicast/Broadcast Single Frequency Network(MBSFN) subframe and a normal subframe can be included together. In thiscase, an independent CFID value can be applied according to whether asubframe including the PDSCH is an MBSFN subframe or a normal subframe.

In other case, depending on whether a subframe is an ABS subframe or anormal subframe, the CFID value can be applied. Also, a subframe isdistinguished according to the amount of interference of a neighboringcell, and the CFID value can be applied accordingly. In other words, theCFID value applied in the serving cell is varied according to whetherthe subframe of a neighboring cell is an ABS subframe or a normalsubframe.

Also, a time period to which a CFID value included in an RRC message isapplied can be determined. The time period may be one frame or multipleframes. In other words, a pattern, based on which the starting positionof the PDSCH is determined with respect to one or multiple frames, canbe informed. The pattern can be provided in a form of index whichdesignates any one of a plurality of predefined patterns.

II. Method 2: A Wireless Communication System can Use a CFID Having aPredefined, Fixed Value.

For example, this method uses a CFID value which takes account of themaximum number of OFDM symbols indicating existence of the PDCCHdepending on characteristics of a subframe. The maximum number of OFDMsymbols indicating existence of the PDCCH in the LTE system is definedby the initial four OFDM symbols within a subframe. Therefore,independently of how many OFDM symbols are involved to form an actualPDCCH, it is always assumed that the PDSCH starts from the fifth OFDMsymbol. Similarly, if the maximum number of OFDM symbols indicatingexistence of the PDCCH in a given frequency band is 3, it can be assumedthat the PDSCH starts from the fourth OFDM symbol.

Since the PDCCH may not present in an ABS frame, the CFID can be setfrom the first OFDM symbol. In other case, the CFID can be set from thesecond OFDM symbol by considering the minimum value of CFI, 1.

III. Method 3: The Base Station can Command a CFID Value on the PDCCH.

For example, the base station can transmit the CFID value byincorporating it into the DCI transmitted through the PDCCH.

In the case of bundled scheduling, one CFID value can be assigned to thewhole or a group (subframe 0 to 2 of FIG. 8(a)) of scheduled subframes,or the CFID value can be assigned independently to each subframe.

In the case of cross subframe scheduling, the CFID value can be definedfor a subframe to which the PDSCH is transmitted.

IV. Method 4: The PCFICH Value in a Subframe to which the PDCCH has beenTransmitted is Used as it is.

The CFI value detected through the PCFICH in a subframe from which thePDCCH is transmitted is applied the same to the subframes in a pluralityof subframe sections. For example, the CFI value of the PCFICH detectedat subframe 0 of FIG. 8(a) is applied the same to the subframe 1 and 2.When this method is employed, the base station may be restricted suchthat the CFI values of the subframe 1 and 2 need to be set the same asthe CFI value of the subframe 0.

In case the PDCCH and the PDSCH belong to the same subframe when themethods above are employed, the CFI value received through the PCFICH isapplied, and a combination of the above methods can be used for othercases. In other words, in case the PDSCH is scheduled in a plurality oftime periods by using one PDCCH; and the PDCCH and PDSCH belong to thesame subframe, the starting position of the PDSCH is identified by thePCFICH as done in a conventional method, but for the remaining subframesexcluding the same subframe from among the plurality of time periods, amethod for identifying the starting position of the PDSCH according tothe present invention can be used.

The above method can be applied the same to the case of scheduling byusing an ePDCCH. However, in case the starting position of an OFDMsymbol of the ePDCCH does not rely on the PCFICH, it is more preferablenot to use the above method.

Also, in case scheduling is performed by using the ePDCCH, the startingposition of the PDSCH transmitted to the same subframe as the one towhich the ePDCCH is transmitted can use the same value as the startingposition of the ePDCCH.

Also, selection of methods I to IV described above can be signaled bythe base station. For example, the base station can specify through RRCsignaling that a method using the PCFICH and a method for using apredefined starting position are applied selectively. Also, the presentinvention can be applied to the case of a scheduled PDSCH or a RandomAccess Response (RAR). For example, in the case of a PDSCH which is setperiodically without the corresponding PDCCH as an SPS is applied, usingthe PCFICH may become unstable if a method for reducing inter-cellinterference in units of subframes in a heterogeneous network is used.Therefore, the starting position of a PDSCH in a subframe which includesthe PDCCH activating/deactivating the SPS is set based on the PCFICH,and the method I or II described above can be applied only to the caseof a PDSCH without the corresponding PDCCH.

Also, the present invention can be applied to the case where ascheduling PDCCH and a scheduled PDSCH are present in a different CCrespectively or to the case of the PDSCH without a scheduling PDCCH.

According to the present invention, since the starting position of thePDSCH is correctly recognized, decoding performance of the PDSCH can beimproved and unnecessary re-transmission can be reduced. As a result,system performance can be enhanced.

In the previous description, it is assumed that the PDCCH corresponds tothe control channel, but the present invention is not limited to theassumption. In other words, a wireless communication system can applythe present invention to the case where the ePDCCH is used as thecontrol channel; or the PDCCH and the ePDCCH are used jointly.

Subframes where the ePDCCH is transmitted can be configured continuouslyor discontinuously. That is, the UE has to detect the ePDCCH incontinuous subframes or in discontinuous subframes.

In case bundled scheduling through the ePDCCH is used, a target ofbundled scheduling by the UE can be limited to DL subframes searchingfor the ePDCCH excluding the DL subframes which do not perform a searchfor the ePDCCH.

For example, suppose data channels of a total of four subframes arescheduled (bundled scheduling) through one ePDCCH. In this case, the oneePDCCH can include information notifying that the number of subframeswhich are a target of bundled scheduling is four. At this time, the fourdenotes 1) four subframes searched by the UE for the ePDCCH or 2) foursubframes from a subframe including the one ePDCCH.

In the case of 1), subframes not searched by the UE for the ePDCCH areskipped and thus a total of four subframes are scheduled. On the otherhand, in the case of 2), if there is one subframe not searched for theePDCCH from among four subframes starting from a subframe including theone ePDCCH, the subframe is excluded and only the remaining threesubframes are scheduled.

In case cross-subframe scheduling is carried out through the ePDCCH, asubframe not searched for the ePDCCH (or a subframe searched for thePDCCH) is skipped and not considered for scheduling. Now suppose thatthe number of subframes scheduled by the ePDCCH is 1 and a scheduledsubframe is a subframe with a subframe offset of 4 from the subframeincluding the ePDCCH. Then the subframe offset 4 can imply the positionafter four subframes searched by the UE for the ePDCCH or the positionafter four subframes determined independently of whether the subframesare those searched by the UE for the ePDCCH.

FIG. 10 illustrates a structure of a base station and a UE according toan embodiment of the present invention.

The base station 100 comprises a processor 110, a memory 120, and aRadio Frequency (RF) unit 130. The processor 110 implements a proposedfunction, procedure and/or method. For example, the processor 110informs the UE about starting positions of data channels located in aplurality of subframes. The methods 1 to 4 can be used as specificimplementation thereof. Also, the processor 110 transmits to the UE acontrol channel and at least one data channel scheduled by the controlchannel. The memory 120, being connected to the processor 110, storesvarious kinds of information for driving the processor 110. The RF unit130, being connected to the processor 110, transmits and/or receives aradio signal.

The UE 200 comprises a processor 210, a memory 220, and an RF unit 230.The processor 210 implements a proposed function, procedure and/ormethod. For example, the processor 210 receives position informationinforming about the starting positions of data channels in a pluralityof subframes and receives a control channel from a downlink subframe.And the processor 210 receives at least one data channel scheduled bythe control channel among a plurality of downlink subframes. At thistime, the starting position of a data channel within the plurality ofdownlink subframes can be determined based on the position information.The memory 220, being connected to the processor 210, stores variouskinds of information for driving the processor 210. The RF unit 230,being connected to the processor 210, transmits and/or receives a radiosignal.

The processor 110, 210 can include Application-Specific IntegratedCircuit (ASIC), other chipsets, logical circuits, data processingapparatus and/or a converter converting a baseband signal to a radiosignal and vice versa. The memory 120, 220 can include ROM (Read-OnlyMemory), RAM (Random Access Memory), flash memory, memory card, storagemedium, and/or other storage apparatus. The RF unit 130, 230 can includeone or more antennas transmitting and/or receiving a radio signal. Incase an embodiment is implemented in the form of software, the methoddescribed in this document can be implemented in the form of a module(procedure, function, and the like) carrying out the aforementionedfunctions. The module can be stored in the memory 120, 220 and executedby the processor 110, 210. The memory 120, 220 can be implemented insideor outside the processor 110, 210 and can be connected to the processor110, 210 through various other means well-known to the public.

So far, the present invention has been described with reference toembodiments; however, it should be understood by those skilled in theart that the present invention can be revised and modified in variousways without departing from the technical principles and scope of thepresent invention. Therefore, it should be noted that the presentinvention is not limited to the embodiments described in this documentbut includes all of the embodiments that can be defined by the appendedclaims of this document.

What is claimed is:
 1. A method for determining a starting orthogonalfrequency division multiplexing (OFDM) symbol for a data channel in atime domain, the method performed by a user equipment (UE) andcomprising: receiving position information, wherein the positioninformation is used only in a specific subframe; and receiving aphysical downlink shared channel (PDSCH), wherein, in the specificsubframe, if the PDSCH is assigned by a physical downlink controlchannel (PDCCH) which is located in the specific subframe, the UEdetermines a starting OFDM symbol for the PDSCH by a physical controlformat indication channel (PCFICH), and wherein, in the specificsubframe, if the PDSCH is not assigned by a control channel which islocated in the specific subframe, the UE determines a starting OFDMsymbol for the PDSCH by the position information instead of the PCFICH.2. The method of claim 1, wherein the position information is receivedby a higher layer signal.
 3. The method of claim 1, wherein the positioninformation is received through a radio resource control (RRC) message.4. The method of claim 1, wherein the specific subframe is a subframe inwhich the UE is configured to monitor an enhanced physical downlinkcontrol channel.
 5. The method of claim 1, the PCFICH indicates a numberof OFDM symbols used for the PDCCH.
 6. A User Equipment (UE), the UEcomprising: a Radio Frequency (RF) unit transmitting and receiving radiosignals; and a processor, connected to the RF unit, that: controls theRF unit to receive position information, wherein the positioninformation is used only in a specific subframe; and controls the RFunit to receive a physical downlink shared channel (PDSCH), wherein, inthe specific subframe, if the PDSCH is assigned by a physical downlinkcontrol channel (PDCCH) which is located in the specific subframe, theUE determines a starting OFDM symbol for the PDSCH by a physical controlformat indication channel (PCFICH), and wherein, in the specificsubframe, if the PDSCH is not assigned by a control channel which islocated in the specific subframe, the UE determines a starting OFDMsymbol for the PDSCH by the position information instead of the PCFICH.7. The UE of claim 6, wherein the position information is received by ahigher layer signal.
 8. The UE of claim 6, wherein the positioninformation is received through a radio resource control (RRC) message.9. The UE of claim 6, wherein the specific subframe is a subframe inwhich the UE is configured to monitor an enhanced physical downlinkcontrol channel.
 10. The UE of claim 6, the PCFICH indicates a number ofOFDM symbols used for the PDCCH.